Manufacture of cements from calcium sulphate and blast furnace slag



- e. cowosmous.

10 comma R M A or both. The exciter chiefly use 111 v ments is Bgztlagdcement clinker, which liberates lime during setting. e general functionof in Dunn et 9.1. U. S. application Serial No. 257,816,

Patented July 1, 1941 MANUFACTURE OF CEMENTS FROM CAL- CIUM SULPHATE ANDBLAST FURNACE SLAG Nelson Elliot Wallace, Norton-on-lees, and VictorLefebure, London, England, assignors to 1mperial Chemical IndustriesLimited, a corporation of Great Britain No Drawing. Application February23, 1939, Se-

rial No. 257,818. In Great Britain February 22,

3 Claims. (Cl. 106-85) (Granted under the provisions of sec. 14, act ofMarch 2, 1927; 357 0. G. 5)

This invention relates to cements obtained from namely cementscomprising blast furnace slag, calcium sulphate and granulated blastfurnace W 'firodiiclnge rciter (in this caseiPg'r'tland cement Blastfurnace slag is the molten non-metallic manna which at least 60 percent. of the by-product obtained during the production of 5slagparticles, at least 50 per cent. of the exciter iron in a blastfurnace, and it is granulated by particles, and at least 60 per cent. ofthe final rapid cooling, e. g. by running a stream of slag mixed cementparticles, are of diameter not exinto water. The slagis thusobtainedl'rfa glassy ceeding 30 microns. As the galgiurn sulphate ornon-crystalline form possessing hydraulic or constituent of the cementwe prefer to employ water-setting properties, especially when mixednatural nh drite.

withan exciter such as an alkali a sulphate, The lone. lime may be m eseous ways, among w ch we have found the folow g be very eifective:

(a) By curing the setting cement in lime water (b) By addition to thecement of groun drated lirn which has been allowed to set 0 a solid masswith water, and subsequently crushed or ground mtively coarse particlesarithis exciter" is to produce and accelerate optimum setting conditionsand strength. particularly early strength. '1"

It has been found that increase in the proportion of Portland cementclinker above a certain (0) By addition of ground set Portland cementlimit causes the cement to become weaker. It 29 to the cement m wouldthus be expected that a well proportioned (d) By the addition ofpartially set Portland cement of this type contained the maximum cemg tothe cement amount of lime for optimum development of e yaddition ofcrushed sand/lime bricks to the cement Tfardnessand strength. One objectof the present invention is still fur- 2.5 ther to increase the strengthof cements of the kind described. A further object is to increase r Ifdesired the substances 131-11) inclusive the surface hardness of suchcements.

Wh'ave now found that the addition of lime b u ed in ub titution for -1;of th tto the setting cement in such a form as to make 30 and ce'fiie vi it available in the later sta es of setting pronu diti or as coarseHuces stronger and Harder cements, even though they contain already theoptimum proportions of clinker.

According to the presen invention, therefore, we improve the strengthand hardness of cements comprising last furnace slag, calcium sul hateand Portland emen 1' r, by allowing the cemen 0 set in the presence ofadditional e to the cement.

ticles.

The following example illustrates the advantage of curing the settingcement in lime water.

Example] A cement was prepared containing 85 parts by weight of groundgranulated l last furnace slag, 15 parts of anhydrite and 5.4' partsPortland lime ri f a llqllia 1585mm in 333355? 40 cement clinkeif'i'wdsamples of the setting cem ii efit'wf iured in water and in limewater re- In P roaucmgu substansrce PF PL mi spectively. Thetensilstrengths v'EFFaTffider:

or an cement c m er a e he mix. -"The invention includes cements of thekind described to which have been added lime-containing orlime-producing substances (other than Portland cement); also mouldedobjects and masses made from the said cements.

Tensile strength {lbs/sq. in.)

After 3 After 7 After 28 days days days In carrying out the invention wepref r ly Cured in eight: 280 445 485 employ cements of the kinddescribed and claimed 350 on calcium sulphate and a lime-ofitainingforlime- (j) By addition of crushed calcium sul hate (plaster of Paris)containing 10-55% calcium Examiner lime.

The following example illustrates the increased surface hardnessobtained by the use of additions of crushed set calcium sule containinExample A mixture was made up of ten parts by weight of plaster offal-isto one part of hydrated lim e. It was allowed Efiet and was then crushedto pass the No. 52 B. S. S. sieve and be retained on the No. 100 B. S.S. sieve. Twenty per cent. of this was added to a calcium sulphate-slagcement containing ortland cement as lagciten" Neat and 3:1 sandciiien't'bars were made'fnd their surface hardness was compared withsimilar bars made from calcium sulphate-slag cement without the additionof the lime containing particles. In the following table are givenmeasurements of the diameter of the depression produced by a Brinellhardness punch; the smaller the diameter, the harder is the surface.

Punch impression in mm. after- 3 days 7 days 28 days With addition.Without addition With addition.... Without addltion.....

In this case, the difference in surface hardness between 3:1 mortarstored in fresh and in lime water was estimated by scratching thesurface of the mortar with a nail and awarding a mark Cal based on theimpression of hardness gained. As an example, the following marks wereawarded.

As many apparently widely different embodiments of this invention may bemade without departing from the spirit and scope thereof, it is to beunderstood that the invention is not limited to the specific embodimentsthereof except as defined in the appended claims.

We claim:

1. A method of improving the strength and hardness of cements comprisinggranulated blast furnace slag, calcium sulphate and Portland cementclinker, which comprises gauging the cement with water, allowing it topartially set, and treating the partially set cement with a liquidmedium containing lime.

2. A method according to claim 1, in which th setting cement is treatedwith lime water.

3. A method of improving the strength and hardness of cements comprisinggranulated blast furnace slag, calcium sulphate and Portland cementclinker, in which at least 60 per cent of the slag particles, at leastper cent of the Portland cement particles, and at least per cent of thefinal mixed cement particles are of diameter not exceeding 30 microns,which comprises gauging the cement with water, allowing it to partiallyset, and treating the partially set cement with a liquid mediumcontaining lime.

NELSON ELLIOT WALLACE. VICTOR LEFEBURE.

